Only a few dielectric materials are useful for high performance electronic applications. To be useful for high speed interconnects, a material must have a low dielectric constant, low loss, and must be capable of adhering to the other materials that it may interface, such as copper, chrome, zinc, aluminum, silicon oxide, silicon nitride (SiN), titanium nitride (TiN), plasma enhanced oxide (PEOX), phosphor-silicate glass (PSG), and the like. Also, the materials must be processable using typical manufacturing techniques, such as spin-on coating, die coating, chemical mechanical polishing, dry etch, imaging, laser ablation, hot/cold press, etc. Other desirable material properties include low moisture absorption, outstanding chemical resistance, good thermal properties, predictable dimension movement, controllable melt flow viscosity, and fracture resistance to cyclic stress.
Advanced high density, multilayer electronic packages require advanced dielectric materials, especially in the high frequency (GHz) applications. One of the key properties for such advanced dielectrics is the low dielectric loss in the GHz frequency range, where associated signal loss becomes a key performance roadblock. To have low dielectric loss, the dielectric materials must have low polarity as well as low dipole moment. Another key requirement is that the glass transition temperature (Tg) of the dielectric materials must be sufficiently high, e.g., higher than 200° C., to survive increasing high temperature manufacturing processes, such as lead-free solder reflow. Other requirements include excellent gap-fill properties, toughness (good elongation), low coefficient of thermal expansion (CTE), e.g., a CTE close to that of copper, (CTE of 17 parts per million (ppm)/° C.), and good adhesion to different bonding treatments applied to other layers.
A dielectric material frequently used for high frequency microwave (e.g., 2.4 GHz) applications is one of a variety of composites based on a fluoropolymer material sold under the trade name TEFLON, such as TEFLON/ceramic, TEFLON/fiberglass, etc. However, TEFLON materials require a high lamination temperature, i.e., over 350° C. Also, due to the non-crosslinked nature (thermoplastic) of TEFLON materials, dimensional stability issues arise when an outside layer is laminated to previous layers. Polyimides, and some polyesters (e.g., aromatic liquid crystal polymers) are also dielectric with good electrical properties, but these polymer-based dielectric materials have issues with moisture uptake, flow-fill, or high CTEs (greater than 60 ppm/° C., especially in Z-axis), which again limit the materials to certain applications. Benzocyclobutene (BCB) polymers are now also becoming known as useful dielectric compounds.
U.S. Pat. No. 6,514,872 B1 discloses a method for manufacturing a semiconductor device in which a benzocyclobutene serves as an inter layer dielectric (ILD). The BCB coating, in a thickness range from 5 μm to 8 μm, is spin-coated onto the desired surface and then patterned anisotropically with a mixture of Cl2/BCl3/O2 using SiO2 film as an etch mask.
U.S. Pat. No. 6,410,414 B1 discloses a method for fabricating a semiconductor device in which a benzocyclobutene film serves as an insulator between redistribution wiring and an alpha particles blocking layer between sensitive integrated circuit devices, such as a memory cell, and an alpha particle source such as a solder ball. The BCB coating, having a thickness range from 10 μm to 100 μm, is spin-coated onto the desired surface.
U.S. Pat. No. 6,294,741 B1 discloses a multi chip module (MCM) package using benzocyclobutene polymer as a laminate adhesive in the construction of such structure. The BCB polymer is first spin-coated onto frame polyimide film sold under the trade name KAPTON E in a layer thickness from 5 μm to 15 μm, and then baked and laminated for making multi-layer interconnect structure.
U.S. Pat. No. 6,262,376 discloses a process for building up high frequency chip carrier substrate on a printed wiring board (PWB) or multi-layer ceramic (MLC) base, in which a polyimide film, or benzocyclobutene film, or a thermoplastic film, with dielectric constant less than 3.0, serves as an insulator on the upper conductor layer(s). The process deposits the dielectric film using either spin-on coating, or chemical vapor deposition (CVD).
U.S. Pat. No. 6,420,093 discloses a process for buildingup printed wiring boards on thick printed circuit board (PCB) cores using metal foil coated with toughened benzocyclobutene-based dielectric polymers. The process laminates a sheet with a metal foil and a BCB-containing dielectric material. The BCB polymers disclosed comprise ethylenically unsaturated polymer additives and photoactive compounds. A partially polymerized “b-stage” material is also disclosed. However, use of fillers is not disclosed. Due to the non-polar nature of the BCB materials and the non-polar solvents, such as mesitylene, used in BCB systems, the polymers are not normally compatible with inorganic filler particles such as silica.
To date, most of the applications involving BCB material use spin-on coating of the materials, either dry etchable or photo imageable, which contain no fillers. Coating thickness is typically less than 20 μm due to the relatively high curing stress of BCB, which often causes wafer or substrate bowing, and thus makes the wafer/substrate unprocessable in post coating processes.